The age of a panchromatic light emitting diode (LED), called as the revolution of light, has come, and the application range thereof is widening to new fields day by day. Especially, an LED, as a light source, is applied to a wide range of technical fields such as computers, mobile phones, automobiles, and the likes and thus interest on the material filed of color filters related to the LED increases as well.
As a method for adjusting the color of light using an LED light source, there are a method for exhibiting colors by applying properties to a light source itself such as the color temperature/color rendering/power efficiency of the light source, a method for applying a specific color by combining a fluorescent substance in the sealing material of an LED package, and a method for making the LED light source to transmit a color filter and adjusting the color and the size of light according to the properties of the color filter.
Conventionally, LEDs used for lighting are classified into pure white, natural white, and warm white LEDs. The pure white LEDs emit light with color temperature between 5,000 K and 8,000 K (wherein, when an object emits light, the color temperature represents the temperature of a black body which has the same light as that of the object). The natural white LEDs emit light with color temperature between 3,500 K and 4,500 K. The warm white LEDs emit light with color temperature between 2,500 K and 3,500 K. Those LEDs are realized by mainly combining a YAG-based yellow fluorescent substance with a blue LED emitting blue light in the band of 450 nm to 480 nm, and have spectral properties with the highest peak power in the vicinity of a blue spectral region (450 nm to 480 nm) and high peak power successively in a green spectral region (520 nm to 580 nm) and a red spectral region (610 nm to 680 nm).
The fluorescent substance basically has a function which converts blue light into green color or red color, and thus the pure white LEDs have the highest power efficiency and the warm white LEDs have the lowest power efficiency. Generally, natural white LEDs have about 85% of light power compared to that of the pure white LEDs, and power efficiency of the warm white LEDs is about 75% lower than that of the pure white LEDs.
Meanwhile, power efficiency can be reduced when the concentration of the fluorescent substance is adjusted to increase light of a red spectral region for increasing color rendering index representing color reproduction fidelity of lighting light. Generally, it is required that light of a red region has to be secured as much as possible by sufficiently adjusting the concentration of fluorescent substances used for LEDs in order to make the warm white LEDs have color rendering index of 85 to 90 or more. In this case, the power efficiency becomes reduced as much as about 10 to 15% compared to warm white or natural white LEDs with color rendering index of 70 to 80.
Further, conventional LED lighting devices have been used in the manner that an array based on three kinds of LEDs, pure white/natural white/warm white LEDs, is installed in an LED lamp in order to selectively realize a variety of color temperatures such as pure white/natural white/warm white; the natural white and warm white LEDs are turned off when a user needs a pure white LED; the pure white and warm white LEDs are turned off when the user needs a natural white LED; and the pure white and natural white LEDs are turned off when the user needs a warm white LED. In this case, however, the quantity of LEDs used for the lighting devices is tripled compared to an LED lighting device exhibiting a single color, and thus it causes high costs. Further, power efficiency becomes reduced since quantity of light at a vicinity of a green region (500 nm to 550 nm) occupying the major part of the entire quantity of light is reduced in addition to that in a blue region (420 nm to 480 nm) when light of the blue region is reduced and quantity of light in a red region is relatively increased by using a conventional Hi-pass filter for realizing high color rendering index and selective color temperature of the LED lightings.
As a method for changing the color of light by adjusting and converting light properties such as wavelengths or light intensity of LED light sources, there can be a method for combining a fluorescent substance or a color filter with a sealing material. As a coloring dye of the fluorescent substance or the color filter, an anthraquinone dye is used for changing light properties as Korean patent publication No. 2006-55631 and Korean patent publication No. 2010-121494. When the color of light is converted, however, it still has problems of reducing the intensity of a light source, adjusting the contrast thereof by gradation, and converting the intrinsic color of the light source into a specific single color, even in case of converting the color into a different color.